Role of volume in small abdominal aortic aneurysm surveillance

Abstract

Objective: Current management of small abdominal aortic aneurysms (AAAs) primarily involves serial imaging surveillance of maximum transverse diameter (MTD) to estimate rupture risk. Other measurements, such as volume and tortuosity, are less well-studied and may help characterize and predict AAA progression. This study evaluated predictors of AAA volume growth and discusses the role of volume in clinical practice.

Methods: Subjects from the Non-invasive Treatment of Abdominal Aortic Aneurysm Clinical Trial (baseline AAA MTD, 3.5-5.0 cm) with ≥2 computed tomography scans were included in this study (n = 250). Computed tomography scans were conducted approximately every 6 months over 2 years. MTD, volume, and tortuosity were used to model growth. Univariable and multivariable backwards elimination least squares regressions assessed associations with volume growth.

Results: Baseline MTD accounted for 43% of baseline volume variance (P < .0001). Mean volume growth rate was 10.4 cm3/year (standard deviation, 8.8 cm3/year) (mean volume change +10.4%). Baseline volume accounted for 30% of volume growth variance; MTD accounted for 13% of volume growth variance. More tortuous aneurysms at baseline had significantly larger volume growth rates (difference, 32.8 cm3/year; P < .0001). Univariable analysis identified angiotensin II receptor blocker use (difference, -3.4 cm3/year; P = .02) and history of diabetes mellitus (difference, -2.8 cm3/year; P = .04) to be associated with lower rates of volume growth. Baseline volume, tortuosity index, current tobacco use, and absence of diabetes mellitus remained significantly associated with volume growth in multivariable analysis. AAAs that reached the MTD threshold for repair had a wide range of volumes: 102 cm3 to 142 cm3 in female patients (n = 5) and 105 cm3 to 229 cm3 in male patients (n = 20).

Conclusions: Baseline AAA volume and MTD were found to be moderately correlated. On average, AAA volume grows about 10% annually. Baseline volume, tortuosity, MTD, current tobacco use, angiotensin II receptor blocker use, and history of diabetes mellitus were predictive of volume growth over time.

Trial registration: ClinicalTrials.gov NCT01756833.

Keywords: Abdominal aortic aneurysm; Aneurysm growth; Aneurysm volume; CT surveillance.

Copyright © 2021 Society for Vascular Surgery. Published by Elsevier Inc. All rights reserved.

Figures

Figure 1.. Relationship between baseline MTD and volume.

Baseline MTD accounted for 43% of baseline volume variance in all 261 patients.

Figure 2.. Comparison of MTD and Volume in 3D aneurysm models.

Small and large volumes were observed across a range of MTDs.

Figure 3.. Relationship between baseline volume and volume growth and baseline MTD and volume growth.

Baseline volume accounted for 30% of volume growth (A). Baseline MTD accounted for 13% of volume growth (B).

Figure 4.. Comparison of AAA MTD and volume measurements based on crossing MTD thresholds for intervention.

The volume and diameter measurements are plotted with dark symbols for the first imaging that captured subjects exceeding diameter thresholds for repair for females (A) and males (B). These measurements are compared to last follow-up imaging of all other subjects who did not reach diameter intervention thresholds.